1. Field of the Invention
The present invention relates to a vehicle body strength control apparatus that controls the strength of a frame or the like of a vehicle body such that collision energy corresponding to the collision mode and the collision object is suitably absorbed.
Priority is claimed on Japanese Patent Application No. 2004-157695, filed May 27, 2004, and Japanese Patent Application No. 2005-117033, filed Apr. 14, 2005, the contents of which are incorporated herein by reference.
2. Description of Related Art
Conventionally, a body strength control apparatus for controlling the strength of a vehicle body is known that, in order to alter the force resisting a collision load that is received from the front of a vehicle by frames that are aligned in the left-right direction of the vehicle, detects a collision mode using a piezoelectric element or a shape memory alloy as an actuator, or using a movable stiffener or the like, and changes the strength of the frame to correspond to different collision loads (for example, refer to Japanese Unexamined Patent Application, First Publication No. H11-291951). Specifically, in a collision mode in which the collision occurs over an entire front surface of a vehicle (i.e., a full-wrap collision), this apparatus decreases the strength of the frames, while, in a collision mode in which the collision load is concentrated in one frame (i.e., an offset collision), the apparatus increases the strength of the frame.
Moreover, an apparatus is known (for example, refer to Published Japanese Translation No. 2001-504413 of the PCT International Application) that determines whether or not a collision has occurred based on, for example, detection results from an acceleration sensor or the like. When a collision has occurred, in order to accelerate the deformation of the frame, this apparatus damages a portion of a frame so that the strength of the frame is lowered.
However, in the above types of body strength adjusting apparatuses according to the conventional technology, because there is only a short time between the determination of the existence of a collision occurrence or from the result of the detection of the collision mode and a predetermined force opposing a collision load, namely, until the force changes to a collision load, a considerable amount of power is required in order to operate the actuator at high speed, and a rapid response capability is also necessary in the actuator. Because of this, the problem arises that the size of the actuator itself becomes considerable. In addition, because it is essential that the power transfer has low resistance in order to improve the response, in particular, the diameter of the power supply cable is large, and the electrode surface area increases. As a result, the problem also arises that the size of the power battery that supplies power to the actuator is increased.
Moreover, in an apparatus that damages a portion of a frame that relate to the above described conventional technology, when a collision occurs, the strength of the frames is only reduced by a constant predetermined amount, and the problem arises that the strength of the frame cannot be suitably changed in accordance with the extent of the collision and the object of the collision.